The article, Human Body Heat for Powering Wearable Devices: From Thermal Energy to Application, provides the information implied by its title. Authored by Moritz Thielen, Lukas Sigrist, Michele Magno, Christofer Hierold, and Luca Benini, it describes approaches for powering a wearable device, with details on the use of body heat as the source of power.
Another consideration in powering wearable devices is the necessity to impose weight and size constraints, particularly if you initially choose a battery as the source of power. To limit size and weight you should use energy harvesting instead of the battery. The article points out that you can harvest energy from several environmental sources:
Light, using photovoltaics
Movement of the wearer
Radio frequency energy (RF)
Temperature differences using a thermoelectric generator (TEG)
An evaluation of these environmental sources reveals that photovoltaic or RF harvesters limit the application of zero-power wearables to environments where sufficient ambient light or RF emissions is provided to satisfy the energy budget. Movement-based harvesting systems require an active wearer and usually have unstable power generation characteristics. In contrast, the human body is a constant heat source and typically a temperature difference exists between body core and the environment.
